Antidetecting network for pushbutton combination lock



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7 ANTIDETECTING NETWORK FOR PUSHBUTTON COMBINATION LOCK Filed Nov. 1,1967 g ue INVENTOR. fozoarv )f filler/27a ATTUAIVIVS United StatesPatent 3,522,488 ANTIDETECTING NETWORK FOR PUSHBUTTON COMBINATION LOCKEdward M. Tellerman, East Rockaway, N.Y., assignor to ContinentalInstruments C0rp., Lynbrook, N.Y., a corporation of New York Filed Nov.1, 1967, Ser. No. 679,872 Int. Cl. E05b 47/00 US. Cl. 317134 ClaimsABSTRACT OF THE DISCLOSURE An antidetecting network for a combinationlock of the type having a plurality of pushbuttons wherein the actuationof a preselected number, less than all, of said pushbuttons inpredetermined sequence is operable to release said lock. There isprovided switch means in the path of the energizing current for thelocking release mechanism which switch means prevents the flow of suchenergizing current unless all of the pushbuttons have been pushed. Theswitch means is under the control of a relay coil which, so long isenergized, causes the switch means to prevent current flow to therelease mechanism. The relay coil becomes unenergized only after allpushbuttons have been actuated to prevent the detection of theparticular pushbuttons involved in the combination.

BACKGROUND OF THE INVENTION In recent years, coded electrically operatedactuating devices have become more and more popular for use inconnection with locking devices, gradually replacing the conventionalmechanical type combination lock which had been in predominant use. Suchcoded actuated devices are often of the type wherein release orunlocking is accomplished by the actuation of a specific number ofpushbuttons in a preselected sequence. Thus, of a plurality ofpushbuttons presented, it is the actuation of a specified number ofthese, usually less than all, in preselected sequence which etfectuatesrelease of the locking mechanism.

The advantages of such arrangement over the predecessor mechanicalarrangement are as obvious as they are numerous.

An example of an electrical pushbutton actuated locking device of thetype involved herein is fully disclosed in US. Pat. No. 3,242,388 datedMar. 22, 1966 and assigned to the assignee hereof. This patent disclosesin great detail the circuitry associated with an electronic lockingdevice wherein the actuation of a number of pushbuttons in preselectedsequence, in accordance with a preselected particular code, is efiectiveto operate the locking release mechanism. The circuitry as disclosed insaid patent includes numerous safeguards to prevent detection of theparticular combination which has been set. Thus, for example, suchcircuitry includes means for disabling the operation of the device for apredetermined interval upon improper operation thereof. In accordancewith the locking device as set forth in Pat. No. 3,242,388, the correctactuation of the pushbuttons in the sequence as ordained by thepreselected code results in the release of the locking mechanism for anadjustable finite period of time, long enough to permit unlocking of thedoor, after which the release mechanism is automatically renderedinoperative.

While the electronic locking device of the prior art, specifically asexemplified in U.S. Pat. No. 3,242,388, goes a long way in providing asystem whose operating code cannot easily be detected, it does not gothe entire distance. For example, one of the most effective ways ofcompromising the pushbutton operated electronic locking device is by amethod commonly known as dusting. In accordance 3,522,488 Patented Aug.4, 1970 with one type of dusting, the pushbuttons are dusted with achemical before an authorized person operates the pushbutton panel togain access to the unauthorized area. After such authorized person hasgained access, the pushbutton panel is examined, and by simple chemicalanalysis, the particular buttons which have been pushed can easily beidentified, reducing the number of possible combinations to a numbersmall enough to enable detection of the correct combination within arelatively short period of time. Thus, with a ten button pushbuttonpanel and a code utilizing four buttons, providing upwards of 5000possible combinations, the detection of the particular four pushbuttonsreduces the number of possible combinations to 24. If only three buttonsform part of the code, providing for 720 possible combinations, thedetection of the three particular pushbuttons involved reduces thenumber of possible combinations to 6. Thus it is seen that the dustingmethod which results in the identification of the individual pushbuttons involved in the particular code seriously compromises thelocking device as it enables detection of the particular combinationwithin a relatively short period of time.

SUMMARY OF THE INVENTION In accordance with the present invention, theaforementioned disadvantages are obviated. More specifically, inaccordance with the invention, in addition to pushing the requisitenumber of pushbuttons in the predetermined sequence, as preordained bythe code, the operator is required to push all of the buttons before theunlocking mechanism is released.

Thus in accordance with the invention, the operator is first required topush the preselected buttons in the ordained sequence resulting in thepartial completion of the energizing circuit for the unlockingmechanism, such partial completion persisting for a predetermined finiteperiod of time. During such finite period of time, the operator isrequired to push all of the buttons on the pushbutton panels to completethe circuitry for releasing the unlocking mechanism. Accordingly, thepresent invention imposes on the operator the further obligation to pushall of the buttons before the door can be opened. This requirementobviously eliminates the possibility of detecting, as by dusting, theparticular pushbuttons initially required to be pushed to operate therelease mechanism.

In accordance with an alternate form of the invention, complete releaseof the unlocking device for the door is accomplished first by pushingthe requisite pushbuttons in accordance with the preselected code in theproper sequence, followed by the pushing only of those buttons notinvolved in the original coded combination.

BRIEF DESCRIPTION OF THE DRAWING The drawing represents a schematiccircuit diagram of the anti-detecting network in accordance with theinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawing,PBI, PBZ, and PB3 represent three of the pushbuttons provided in anelectronic unlocking device having as many additional pushbuttons (notshown) as may be deemed desirable. In accordance with such electronicunlocking device, the actuation of a preselected number of suchpushbuttons in a preselected sequence is effective to operate the lockrelease mechanism, such unlocking device being fully described inpreviously mentioned Pat. No. 3,242,388. Effectively, the actuation ofthe pushbuttons as ordained by the code, is operative, by means of thecircuitry described in said Pat. No. 3,242,388 to energize an outputrelay (not shown) which in turn controls switch SW2, causing the latterto move from its engagement with contact 12 (as shown in the drawing)into engagement with contact 14. Such actuation of switch SW2 forms acontinuous path through electric door strike operating relay 15 whichpermits opening of the door, provided however that switch SW1 is inengagement with contact 17. Under such conditions, current flow is frompositive terminal 16 through switch SW2, contact terminal 14, switchSW1, contact terminal 17, relay 15 and negative terminal 19. In thedrawing, switches SW1 and SW2 are shown in position corresponding to theunenergized condition of their respective operating relays.

Each of said pushbuttons PBl, PB2, PB3, etc. is a double pole singlethrow switch, one pole of which is used in connection with the unlockingmechanism as aforedescribed, and the other pole of which is shown in thedrawing and is used for the objects of the present invention. Thus, PBl,when actuated, closes contacts 10 thereof, PB2 when actuated closescontacts 2020 thereof, and PB3 when actuated closes contacts 30-30thereof. While only three pushbuttons are shown, it will be understoodthat there are provided as many pushbuttons with circuitry identical tothat shown as may be desired for a particular unlocking device.

Each pushbutton is associated with a condenser, as for example,condenser C1 with pushbutton PBl, condenser C2 with pushbutton PB2, andcondenser C3 with pushbutton PB3. In the position of switch SW2 shown inthe drawing, which corresponds to the unenergized condition of theoutput relay of the electronic unlocking device, there is a continuouspath from positive terminal 16, switch SW2, terminal 12, resistor R18,oneway diode CR1, condenser C1 and negative terminal 22 defining acharging circuit for condenser C1. Similarly, when SW2 is in theposition shown in the drawing, there is a continuous path from positiveterminal 16, switch SW2, terminal 12, resistor R18, one-way diode CR2,condenser C2, terminal 24, terminal 26, and negative terminal 22,defining a charging circuit for condenser C2. In the same manner, acontinuous path exists from positive terminal 16, through switch SW2,terminal 12, resistor R18, one-way diode CR3, condenser C3, terminal 24,terminal 26, and negative terminal 22, defining a charging circuit forcondenser C3. Thus, it is seen that all of the condensers C1, C2., C3,etc. are charged when SW2 engages terminal 12, corresponding to theinoperative condition of the unlocking mechanism.

Q is a conventional transistor amplifier which becomes conductive whenthere is current flow through its emitter. As shown in the drawing,transistor Q is in a conductive state when switch SW2 is in engagementwith contact 12, corresponding to the inoperative condition of theunlocking mechanism. In such condition, there is a continuous path frompositive terminal 16, switch SW2, resistor R18, diode CR1, one-way diodeCR4, (also through parallel paths CR2-CR5 and CR3-CR6), resistor R32 andnegative terminal 34. Such current flow through the emitter oftransistor Q renders the latter conductive to provide a current pathfrom positive terminal 36, relay 38, transistor Q and negative terminal34, causing energization of relay 38. Relay 38, when energized, isoperative to move switch SW1 which is under its control away fromengagement with terminal 17. Thus, the energization of relay 38 preventsthe electric door strike relay from being energized. Conversely, onlywhen relay 38 is unenergized, corresponding to the non-conductive stateof transistor Q, is switch SW1 in engagement with contact 17.Accordingly, in order for the electric door strike relay to beenergized, and for the unlocking of the door to be possible, transistorQ must be non-conductive at the same time that switch SW2 is inengagement with contact 14.

It has been demonstrated above that when switch SW2 is in engagementwith contact 12, transistor Q is conductive whereby switch SW1 is open,preventing the energization of relay 15. When the pushbutton combinationis activated in accordance with the preselected code, SW2 will engagecontact 14, without however interrupting current flow to the emitter oftransistor Q, as such current flow is maintained as a result of thedischarge of condensers C1, C2, C3, etc. More specifically, the chargeon condenser C1 causes current flow from condenser C1 through terminal28, diode CR4, resistor 32, the emitter of transistor Q, negativeterminal 34, negative terminal 26, and back to condenser C1. Suchcurrent flow maintains conductivity in Q to thereby maintaln relay 38energized and switch SW1 open. In this connection, it will be noted thatthe capacitance of C1 and resistance of R2 is such as to provide a totaldischarge time which exceeds the finite period of time during which SW2remains in engagement with contact 14, following a correct actuation ofthe pushbuttons. Accordingly, the discharge of C1, C2, C3, or of any ofthe other condensers prevents energization of the electric door strikerelay. The only way to prevent condenser C1 from discharging andmaintaining triggering current flow for Q is to discharge said condenserinstantaneously by actuation of pushbutton PBl. Such actuation of PBlW111 provide for the instantaneous discharge of condenser C1 throughresistor R36. In order to completely cut 01f triggering current flow,all other condensers must similarly be discharged by actuation of theassociated pushbutton. Thus, in addition to PBl, pushbuttons PB2, PB3and all others in the system will have to be pushed to discharge theirassociated condensers and cut off all trigger current flow. When allsuch trigger current flow has been interrupted, during the time intervalthat SW2 1s 1n engagement with contact 14, Q will become nonconductiveto de-energize relay 38 and place switch SW1 1n engagement with contact17 in order to complete the circuit for energization of electric doorstrike relay 15. It will be noted that one-way diode CR4 prevents thedischarge of all condensers except C1, upon actuation of pushbutton PB1.Similarly, one-way diodes CR5 and CR6 perform a corresponding functionupon actuation of pushbuttons PB2 and PB3, respectively.

From the above, it is clear that, though the preselected pushbuttonshave been actuated, in accordance with the predetermined sequence, it isstill necessary thereafter to actuate all of the pushbuttons before theunlocking mechanism can effectively permit opening of the door. Therequirement to have all pushbuttons actuated thus eliminates thepossibility of detecting the particular buttons which are part of thecode combination.

In the embodiment described above, it is clear that all of thepushbuttons on the panel must be pushed before the door can be openedand this includes the pushing of those buttons which may already havebeen pushed in accordance with the code combination. If the repeatedpushing of the pushbuttons involved in the combination is desired to beeliminated, such can be accomplished in any one a plurality of ways. Asimple way would be to provide a toggle switch immediately in serieswith each condenser, with toggle switch would remain closed for allpushbuttons except only those involved in the particular preselectedcombination. Thus, when the combination for the unlocking mechanism isinitially set, the toggle switches associated with the pushbuttonsinvolved in the combination would be opened, preventing the condensersassociated with the preselected pushbuttons from discharging intotriggering circuit for transistor Q. For example, the toggle switch forpushbutton PBI could be located between C1 and terminal 28 or anywhereelse along the discharge path of said condenser through transistor Q. Inthis manner, the pushbuttons involved in the combination need only bepushed once, for the purpose of energizing the output relay whichcontrols switch SW2.

While I have herein shown and described the preferred embodiments of myinvention, it will be understood that the invention may be embodiedotherwise than as herein specifically illustrated or described, and thatin the illustrated embodiments certain changes in the details ofconstruction and in the form and arrangement of parts may be madewithout departing from the underlying idea or principles of thisinvention within the scope of the appended claims.

Having thus described my invention, what I claim and desire to secure byLetters Patent is:

1. In a combination lock mechanism having a plurality of pushbuttonswherein the actuation of particular preselected pushbuttons less thanall of said pushbuttons in predetermined sequence is operable to actuatea switch in an electrical path forming part of an electrically operatedlock mechanism, the improvement comprising open second switch meansinterposed in said electrical path and preventing current flowtherethrough, and electrical control means closing said second switchmeans in response to the actuation of all of said pushbuttons subsequentto the actuation of said particular ones, whereby failure tosubsequently actuate all of said pushbuttons prevents release of saidlock mechanism.

2. The improvement in accordance with claim 1 wherein said electricalcontrol means comprises a relay coil which, when unenergized, causessaid second switch means to close.

3. The improvement in accordance with claim 2 wherein there is provideda transistor amplifier having its collector connected to said relay coilwhereby the latter can be energized only when said transistor amplifieris in a conducting state.

4. The improvement in accordance with claim 3 .wherein each pushbuttonis associated with a condenser connected in a charging circuit thereforwhich is energized before actuation of said preselected buttons in saidpredetermined sequence.

5. The improvement in accordance with claim 4 wherein each condenser isconnected to the emitter circuit of said transistor whereby uponactuation of said preselected buttons in said predetermined sequenceeach condenser discharges through said emitter circuit to providetriggering current for said transistor.

6. The improvement in accordance with claim 5 wherein each of saidpushbuttons is connected to its associated condenser so as toinstantaneously discharge the latter upon actuation thereof, therebypreventing the associated condenser from discharging through thetriggering circuit of said transistor.

7. In a combination lock mechanism having a plurality of pushbuttonswherein the actuation of particular preselected pushbuttons less thanall of said pushbuttons in predetermined sequence is operable to actuatea switch in an electrical path forming part of an electrically operatedlock mechanism, the improvement comprising open second switch meansinterposed in said electrical path and preventing current flowtherethrough, and electrical control means closing said second switchmeans in response to the actuation of the pushbuttons other than saidparticular ones subsequent to the actuation of said particular ones,whereby failure to sub sequently actuate the pushbuttons other than saidparticular ones prevents release of said lock mechanism.

8. The improvement in accordance with claim 7 wherein said electricalcontrol means comprises a relay coil which, when unenergized, causessaid second switch means to close.

9. The improvement in accordance with claim 8 wherein there is provideda transistor amplifier having its collector connected to said relay coilwhereby the latter can be energized only when said transistor amplifieris in a conducting state.

10. The improvement in accordance with claim 9 wherein each pushbuttonis associated with a condenser connected in a charging circuit thereforwhich is energized before actuation of said preselected buttons in saidpredetermined sequence.

References Cited UNITED STATES PATENTS 3,242,388 3/1966 Teller-man317134 3,383,887 5/1968 Harris et a1. -313 X 3,441,808 4/1969 Crane317134 J. D. MILLER, Primary Examiner W. J. SMITH, Assistant ExaminerUS. 01. X.R.

